EP3427285B1 - Device for modulating the intensity of a charged particle beam, method for deviating a charged particle beam from the axis of emission with said device and system including this device. - Google Patents

Description

Technical field of the invention

The invention relates to the technical field of instruments producing charged particle beams in an energy range from 1 eV / charge to several 10 ¹² eV / q.

• équipement des accélérateurs de particules
• implantation ionique (traitement de surface etc...)
• médical (hadronthérapie, production radioisotope, nanomédicaments...)
• dépôt sous vide
• micro-gravure
• propulsion ionique pour engins spatiaux
• spectromètre de masse par accélération pour l'analyse d'échantillon,
• datation

Instruments of this type find applications in many fields depending on the charge, mass, kinetic energy of accelerated particles:

• particle accelerator equipment
• ion implantation (surface treatment etc ...)
• medical (hadrontherapy, radioisotope production, nanomedicines ...)
• vacuum deposit
• microetching
• ion propulsion for spacecraft
• acceleration mass spectrometer for sample analysis,
• dating

The invention relates more particularly to the modulation of the intensity (or current or the flow of particles) of the beam of charged particles produced in order to modulate the impact on the targeted sample and to be able to vary the possible uses of a same instrument.

State of the art and its drawbacks

• en variant l'intensité de la source de particules chargées
• en collimatant le faisceau à l'aide de pièces mécaniques amovibles (ex : système de fentes, iris)
• en pulsant le faisceau avec différents rapport cycliques.

The beams of charged particles can currently be modulated by current in various ways, in particular:

• by varying the intensity of the source of charged particles
• by collimating the beam using removable mechanical parts (eg slit system, iris)
• by pulsing the beam with different duty cycles.

However, the different techniques presented above pose many technical problems:
The use of pulsed beams is, for example, not applicable in all applications of charged particle beams.

The adjustment of the intensity of the source of charged particles as well as the use of mechanically removable collimators do not meet the reactivity constraints necessary for certain applications.

In the example of the document US 8,896,238 , one manages to modulate the current of a beam of an ion source generating a curved ion beam within a particular accelerator of cyclotron type. The intensity modulation of this beam is carried out using a Dee electrode connected to a high frequency generator which applies to the Dee electrode an alternating high voltage of an amplitude which can be modulated by a regulator. The ions are accelerated between the Dee electrode and a counter electrode connected to ground, through a gap and define, due to the application of voltages of different amplitudes on the Dee electrode, circular paths of different rays. A full screen arranged at a distance from the counter-electrode delimits with the latter a passage space for the ions having a trajectory of a curvature exceeding a critical value, and defines an obstacle for the ions whose curvature is below this value critical. The modulation of the amplitude of the voltage applied to the Dee electrode which modifies the different trajectories of the ions, combined with the presence of the screen, makes it possible to modulate the number of ions and thus the current ultimately emitted by the source.

However, this device is specific to charged particles with curved paths emitted by a cyclotron source and cannot be transposed to a device emitting a beam of linear charged particles.

The document US 3,286,123 relates to a device for emitting a linear particle beam. In this device, under the effect of a perforated electrode, a deflection system and multiple lenses distributed along the axis of their emission, and the presence of a deflector, the beam of charged particles is deviated from its initial trajectory according to variable profiles depending on the position and the focal length of the lenses and some may be collected by a collector placed perpendicular to the axis of the emission of the particles. The applications of this device are however not compatible with those targeted by the invention, the charged particle beam being definitively deviated from its initial axis and not recoverable at a given fixed location.

• le document EP 2592642 concerne un dispositif d'émission d'un faisceau de particules chargées comprenant une succession d'éléments octopolaires (302, 304, 306, 308) susceptibles d'être le siège d'excitations dipolaires, quadripolaires et hexapolaires, les deux premiers éléments permettant une dispersion en hauteur et en énergie du faisceau, les deux éléments centraux étant séparés par un collimateur pourvu d'un orifice en forme de fente laissant passer une portion des particules d'une énergie donnée et interceptant les autres. Ce dispositif permet ainsi de moduler l'énergie du faisceau de particules chargées mais pas l'intensité du faisceau sortant qui reste sensiblement la même,
• par ailleurs, le document US 8039822 concerne un appareil de thérapie par particules comportant un accélérateur pour générer un faisceau de particules chargées, un modulateur d'énergie passive comprenant un élément absorbant et une entité de commande. L'entité de commande est conçue pour commuter entre un ajustement actif de l'énergie contenue dans l'accélérateur et une modulation de l'énergie passive par le modulateur d'énergie, dans le but de modifier l'énergie du faisceau de particules chargées à partir d'un niveau d'énergie élevé à un faible niveau d'énergie dans une étape par étape manière. En particulier, cela a pour effet de raccourcir les temps morts lors d'un changement entre les niveaux d'énergie mais toujours pas la possibilité de moduler l'intensité du faisceau sortant.

Other devices generating beams of linear charged particles and provided with modulation means are known but this modulation is carried out on the energy of this beam and not on the current (the quantity) of particles:

• the document EP 2592642 relates to a device for emitting a charged particle beam comprising a succession of octopolar elements (302, 304, 306, 308) capable of being the seat of dipolar, quadripolar and hexapolar excitations, the first two elements allowing a dispersion in height and in energy of the beam, the two central elements being separated by a collimator provided with an orifice in the form of a slit allowing a portion of the particles of a given energy to pass and intercepting the others. This device thus makes it possible to modulate the energy of the beam of charged particles but not the intensity of the outgoing beam which remains substantially the same,
• moreover, the document US 8039822 relates to a particle therapy apparatus comprising an accelerator for generating a charged particle beam, a passive energy modulator comprising an absorbent element and a control entity. The control unit is designed to switch between an active adjustment of the energy contained in the accelerator and a modulation of passive energy by the energy modulator, in order to modify the energy of the charged particle beam from a high energy level to a low energy level in a step by step manner. In particular, this has the effect of shortening the dead times during a change between the energy levels but still not the possibility of modulating the intensity of the outgoing beam.

The document US 9,224,569 describes a high brightness ion source with a gas chamber which includes different compartments each having a different gas. A beam of electrons is caused, by means of deflection plates, to pass selectively through one of the compartments to supply ions of a certain species for processing a sample. It is possible to easily modify the species of ions supplied by directing the electrons through other compartments containing a different species of gas in order to treat a sample with ions of another species. If the nature of the ions generated is easily and quickly modified, the number of species of ions is reduced to that of the number of compartments of the gas chamber, and the possible different intensities of the beams of different possible ions, are also reduced to number of room compartments. This system does not allow a continuous modification of the intensity of the beam supplied.

The document US 2009/0050819 A1 discloses a compact particle selection and collimation device for delivering proton beams with desired energy spectra.

No satisfactory solution has therefore yet been found to modulate in intensity and continuously the beam of charged particles emitted by a source supplying a linear accelerator.

Statement of the invention

The invention aims to solve this problem by proposing a device for modulating the intensity of a beam of charged particles according to claim 1.

• chacun desdits systèmes de déviation est de type électrique ou de type magnétique
• lorsque les systèmes de déviation sont de type électrique, chaque système est constitué de deux plaques parallèles portées à un potentiel électrique et disposées respectivement de part et d'autre de l'axe d'émission A0.
• lorsque les systèmes de déviation sont de type magnétique chacun desdits systèmes de déviation est constitué par un dipôle magnétique.
• la fente d'un collimateur présente une forme générale de V avec des bords opposés rectilignes ou courbes bombés vers la partie restante du collimateur ou vers l'espace vide délimité par ces bords.
• chaque collimateur est placé le long de l'axe de façon à ce que sa fente soit disposée d'un côté de l'axe d'émission A0 en étant décalée vis-à-vis de cet axe A0 d'une distance d.
• ou chaque collimateur est placé le long de l'axe de façon à ce que sa fente soit disposée dans l'axe d'émission A0
• lorsque le dispositif comprend 8 systèmes de déviation, quatre de ces systèmes sont disposés vis-à-vis de l'axe d'émission de façon à dévier le faisceau émis selon une première direction, et quatre autres de ces systèmes sont disposés vis-à-vis de l'axe d'émission de façon à dévier le faisceau émis selon une deuxième direction perpendiculaire à la première.

The device according to the invention can moreover have one and / or the other of the following characteristics:

• each of said deflection systems is of the electrical or magnetic type
• when the deflection systems are of the electrical type, each system consists of two parallel plates brought to an electrical potential and disposed respectively on either side of the emission axis A0.
• when the deflection systems are of magnetic type each of said deflection systems is constituted by a magnetic dipole.
• the slit of a collimator has a general shape of V with opposite rectilinear or curved curved edges towards the remaining part of the collimator or towards the empty space delimited by these edges.
• each collimator is placed along the axis so that its slot is disposed on one side of the emission axis A0 while being offset with respect to this axis A0 by a distance d.
• or each collimator is placed along the axis so that its slot is arranged in the emission axis A0
• when the device comprises 8 deflection systems, four of these systems are arranged opposite the emission axis so as to deflect the beam emitted in a first direction, and four others of these systems are arranged opposite screw of the emission axis so as to deflect the beam emitted in a second direction perpendicular to the first.

• par le premier système de déviation d'une première force de déviation du faisceau suivant une direction donnée et selon un premier sens,
• par le deuxième système de déviation d'une deuxième force de déviation supérieure à la première, selon la même direction et en sens inverse du premier,
• par le troisième système de déviation du faisceau, de la deuxième force de déviation du faisceau suivant la même direction et selon le premier sens de déviation,
• par le quatrième système de déviation, de la première force de déviation, selon la même direction et en sens inverse du premier.

The invention relates to a method of deflecting its emission axis from a beam of charged particles emitted along an axis A0, using the above device, comprising for 4N successive deflection systems, a step of application :

• by the first deflection system of a first deflection force of the beam in a given direction and in a first direction,
• by the second deflection system of a second deflection force greater than the first, in the same direction and in the opposite direction from the first,
• by the third beam deflection system, the second beam deflection force in the same direction and in the first direction of deflection,
• by the fourth deflection system, from the first deflection force, in the same direction and in the opposite direction from the first.

Ideally, the deflection systems are of the electrical type, and each comprise two plates parallel to the axis A0 and arranged on either side of this axis A0, the potentials applied to the two plates of the same system being symmetrical or asymmetrical.

According to another possible embodiment, each deflection system is composed of two plates arranged on either side of the axis (A0), two or more plates of different deflection systems being earthed, the deflection forces of the beam of the deflection systems of the plates being different, correction factors (Uib) being applied to each deflection force imposed on a deflection system of which one of the plates is grounded in order to correct the exit angle of the beam.

According to another characteristic, additional adjustable deflection forces are applied to one or more deflection systems in order to correct the beam exit angle.

• une source d'émission d'un faisceau de particules chargées centré autour d'un axe d'émission A0, de préférence de type ECR
• un système d'extraction
• une lentille de type Einzel
• un collimateur à orifice central circulaire
• le dispositif de modulation de l'intensité du faisceau en sortie du premier collimateur,
• un deuxième collimateur à orifice central circulaire
• un filtre des particules en sortie du deuxième collimateur, par la vitesse

The invention also relates to an assembly for transmitting a beam of charged particles of adjustable intensity, comprising successively along an emission axis A0 of the beam:

• a source of emission of a charged particle beam centered around an emission axis A0, preferably of the ECR type
• an extraction system
• an Einzel type lens
• a collimator with a circular central orifice
• the device for modulating the intensity of the beam at the output of the first collimator,
• a second collimator with circular central orifice
• a particle filter at the output of the second collimator, by the speed

Presentation of the figures

• la figure 1 représente par une vue en perspective un ensemble d'émission d'un faisceau de particules chargées d'intensité modulable pourvu d'un dispositif de modulation d'intensité selon l'invention
• la figure 2 représente une vue schématique en section longitudinale du dispositif de modulation de la figure 1, mettant en évidence les collimateurs à fentes en V de ce dispositif,
• la figure 3 représente quatre vues analogues à celles de la figure 2 pour différentes tensions appliquées
• la figure 4 illustre par un graphique l'évolution de l'intensité du faisceau I de particules en sortie du dispositif de modulation rapportée à l'intensité de faisceau à l'entrée I0, en fonction de la tension U2 appliquée sur les systèmes de déviation
• la figure 5 représente le dispositif de la figure 2 faisant apparaître les lignes de potentiels appliquées avec des potentiels symétriques (5(a) et des potentiels asymétriques (5(b)
• la figure 6 illustre l'émittance de faisceaux dans le cas de potentiels symétriques (figure 6(a)) et asymétriques (figure 6(b)), l'ellipse représentée correspondant à l'acceptance d'une ligne de faisceau particulière, et mettant en évidence le fait qu'il est possible, en recourant à une asymétrie de potentiels (tous en gardant une symétrie de forces) de corriger les aberrations optiques du dispositif pour rendre le faisceau compatible avec le reste d'une ligne.

Other data, characteristics and advantages of the present invention will appear on reading the following non-limited description, with reference to the appended figures which represent, respectively:

• the figure 1 shows a perspective view of an emission assembly of a beam of charged particles of adjustable intensity provided with an intensity modulation device according to the invention
• the figure 2 represents a schematic view in longitudinal section of the device for modulating the figure 1 , highlighting the V-slot collimators of this device,
• the figure 3 represents four views similar to those of the figure 2 for different applied voltages
• the figure 4 illustrates by a graph the evolution of the intensity of the beam I of particles at the output of the modulation device compared to the beam intensity at the input I0, as a function of the voltage U2 applied to the deflection systems
• the figure 5 represents the device of the figure 2 showing the applied potential lines with symmetric potentials (5 (a) and asymmetric potentials (5 (b)
• the figure 6 illustrates the emittance of beams in the case of symmetrical potentials ( figure 6 (a) ) and asymmetrical ( figure 6 (b) ), the ellipse represented corresponding to the acceptance of a particular beam line, and highlighting the fact that it is possible, by resorting to an asymmetry of potentials (all while keeping a symmetry of forces) to correct the optical aberrations of the device to make the beam compatible with the rest of a line.

Detailed description of an exemplary embodiment

In accordance with the figure 2 , the invention relates to a device for modulating the intensity of a beam of charged particles 1.

This device is arranged downstream of a source of particles of the ECR type, of an extraction system, of a lens of the Einzel type and of a collimator with a circular central orifice with a diameter of 20 mm in the example illustrated. , and upstream of a second collimator with circular central orifice, and possibly of a particle speed filter so that these are used for various applications.

The assembly with source of particles, extraction system, lens and first collimator emits at the output a beam of charged particles of intensity I0 along an axis A0.

• 4xN systèmes de déviation 2, avec N = 1 (ou 2 selon une variante non illustrée), les systèmes de déviation 2 étant placés le long de l'axe de l'émission A0 dudit faisceau de particules,
• des moyens 3 d'application d'une force de déviation du faisceau pour chaque système de déviation 2 (un seul de ces moyens étant schématiquement représenté),
• deux collimateurs à fente en V 4₁, 4₂ placés respectivement entre le premier et le deuxième système de déviation et entre le troisième et quatrième système de déviation, pourvus chacun d'une fente 6₁, 6₂ de passage du faisceau dévié de son axe d'émission, chaque fente 6₁, 6₂ de collimateur présentant une largeur croissante du centre du collimateur vers la périphérie, la fente 6₁ du premier collimateur 4₁ étant disposée d'un côté de l'axe d'émission du faisceau A0, la fente 6₂ du deuxième collimateur 4₁ étant disposée de l'autre côté de l'axe du faisceau A0, les ouvertures des fentes étant orientées en sens inverse l'une de l'autre.

The device for modulating the intensity of the beam of charged particles according to the invention comprises:

• 4xN deflection systems 2, with N = 1 (or 2 according to a variant not illustrated), the deflection systems 2 being placed along the axis of emission A0 of said particle beam,
• means 3 for applying a beam deflection force for each deflection system 2 (only one of these means being diagrammatically shown),
• two V-slit collimators 4 ₁ , 4 ₂ placed respectively between the first and the second deflection system and between the third and fourth deflection system, each provided with a slit 6 ₁ , 6 ₂ for passing the deflected beam of sound emission axis, each collimator slot 6 ₁ , 6 ₂ having an increasing width from the center of the collimator towards the periphery, the slot 6 ₁ of the first collimator 4 ₁ being arranged on one side of the beam emission axis A0, the slot 6 ₂ of the second collimator 4 ₁ being disposed on the other side of the axis of the beam A0, the openings of the slots being oriented in opposite directions to one another.

In the example illustrated in the figures, the deflection systems of the device according to the invention are of the electrostatic type and each consist of two parallel plates 7 arranged on either side of the axis of emission of the beam A0. The plates of the different systems are parallel and equidistant from the axis A0. A potential difference Ui is applied between the two plates 7 of the same system (see in particular figure 3 ) who constitutes for the beam a deflection force F, the deviation from its initial trajectory A0 on one side of this axis A0 in the direction X marked on the figure 3 .

One could also use deflection systems of the magnetic type, which makes the modulation applicable for high energy beams and the applied deflection force would be of the magnetic type, this variant embodiment can be illustrated schematically with the same figures as those used for electrical type deflection systems.

In this first example, the deflection forces applied by the first and fourth systems are equal in absolute value (2 U1) and the forces applied by the second and third system are equal in absolute value (2U2) in order to bring the beam back on the axis A0 at device outlet.

1. 1) Lorsque le faisceau de particules chargées traverse le premier système de déviation 21, il est dévié d'un côté de l'axe (côté positif de l'axe X de la figure 2) par la force de déviation F exercée par ce premier système (U1/-U1).
   Cette déviation amène le faisceau à hauteur de la fente 6₁ du premier collimateur 4₁ qu'il rencontre sur son passage.
   Ce premier collimateur 4₁ présente conformément à la figure 2, la forme d'une plaque circulaire dans l'exemple illustré mais pouvant bien entendu présenter d'autres formes, définissant un centre C coïncidant avec l'axe d'émission du faisceau A0 lorsque le collimateur est monté perpendiculairement à l'axe d'émission du faisceau A0, et pourvue d'une fente en forme général de V, dont la pointe est décalée d'une distance d au dessus du centre C et ainsi de l'axe d'émission A0 suivant la direction de la force de déviation.
   En fonction de la force de déviation F1 appliquée par le premier système 2₁ sur le faisceau, celui-ci sera plus ou moins dévié d'un côté (au-dessus) de l'axe d'émission A0 et une plus ou moins grande section de ce faisceau traversera la fente, le reste étant intercepté par la plaque du premier collimateur 4₁.
2. 2) La portion de faisceau dévié et sortant du premier collimateur 4₁ débouche alors au niveau du deuxième système de déviation 2₂ qui est le siège d'une force de déviation F2 (-U2/U2) en sens inverse de celle du premier système, et d'amplitude plus importante que celle-ci afin de dévier cette portion de faisceau de l'autre côté de l'axe démission A0 (en dessous).
3. 3) La portion de faisceau du côté négatif de l'axe X débouche au niveau du troisième système de déviation 2₃ qui est le siège d'une force de déviation F3 en sens inverse de celle du deuxième système (U2/-U2), et d'amplitude égale ou équivalente afin de dévier la portion de faisceau vers l'autre côté de l'axe X (vers le côté positif tout en restant du côté négatif) à proximité de l'axe A0.
   Cette portion de faisceau rencontre en sortie du troisième système de déviation 2₃, le deuxième collimateur 4₂ pourvu d'une fente en V 6₂ dont l'ouverture est orientée à l'opposé de celle du premier collimateur (c'est-à-dire dans l'exemple illustré, vers le côté négatif de l'axe X) pour plus ou moins laisser passer de particules en fonction des forces de déviation des systèmes précédents.
4. 4) Le dernier système de déviation 2₄ est le siège d'une force de déviation F4 ((-U1/U1) qui vient ramener le faisceau « rogné » par les deux fentes 6₁, 6₂ précisément dans l'axe d'émission initial A0. Son sens est inverse de la force exercée par le système de déviation précédent et son amplitude moindre.

In addition, the voltages U1 and U2 are according to this first example, in the following relation: 3U1 = U2.

1. 1) When the beam of charged particles crosses the first deflection system 21, it is deflected on one side of the axis (positive side of the X axis of the figure 2 ) by the deflection force F exerted by this first system (U1 / -U1).
   This deflection brings the beam up to the slot 6 ₁ of the first collimator 4 _{1 which} it encounters in its path.
   This first collimator 4 ₁ presents in accordance with the figure 2 , the shape of a circular plate in the example illustrated but may of course have other shapes, defining a center C coinciding with the axis of emission of the beam A0 when the collimator is mounted perpendicular to the axis of emission of the beam A0, and provided with a generally V-shaped slot, the point of which is offset by a distance d above the center C and thus from the emission axis A0 in the direction of the deflection force .
   Depending on the deflection force F1 applied by the first system 2 ₁ to the beam, it will be more or less deflected to one side (above) of the emission axis A0 and a greater or lesser section of this beam will pass through the slit, the rest being intercepted by the plate of the first collimator 4 ₁ .
2. 2) The portion of beam deflected and leaving the first collimator 4 ₁ then emerges at the level of the second deflection system 2 ₂ which is the seat of a deflection force F2 (-U2 / U2) in the opposite direction to that of the first system, and of greater amplitude than this in order to deflect this portion of beam on the other side of the emission axis A0 (below).
3. 3) The portion of the beam on the negative side of the X axis opens at the third deflection system 2 ₃ which is the seat of a deflection force F3 in the opposite direction to that of the second system (U2 / -U2), and of equal or equivalent amplitude in order to deflect the beam portion towards the other side of the X axis (towards the positive side while remaining on the negative side) near the A0 axis.
   This portion of the beam meets at the outlet of the third deflection system 2 ₃ , the second collimator 4 ₂ provided with a V-shaped slot 6 ₂ whose opening is oriented opposite to that of the first collimator (that is to say - say in the example illustrated, towards the negative side of the X axis) to more or less allow particles to pass depending on the deflection forces of the previous systems.
4. 4) The last deflection system 2 ₄ is the seat of a deflection force F4 ((-U1 / U1) which brings the beam "cropped" by the two slits 6 ₁ , 6 ₂ precisely in the axis of initial emission A0, its direction is opposite to the force exerted by the previous deflection system and its lesser amplitude.

• dans l'exemple de la figure 3(a), la totalité des particules est stoppée du fait du lieu d'arrivée du faisceau sur chaque collimateur (la portion de faisceau ayant traversé la première fente 61 ne traverse pas la deuxième fente 62 mais est interceptée par le collimateur 42 car elle atteint le collimateur au-dessus de la deuxième fente)
• dans l'exemple de la figure 3(c), la quasi-totalité des particules traverse le dispositif (la quasi-totalité des particules traverse la première fente, et la quasi-totalité de la portion de faisceau sortant du premier collimateur traverse la deuxième fente)
• les exemples des figures 3(b) et 3(d) illustrent des situations intermédiaires entre les situations 3(a) et 3(c).

In accordance with the figure 3 , the variation of the potentials applied (or beam deflection force applied) by each of the deflection systems, allows the intensity of the beam at the device output to be varied:

• in the example of the figure 3 (a) , all of the particles are stopped because of the place of arrival of the beam on each collimator (the beam portion having passed through the first slot 61 does not pass through the second slot 62 but is intercepted by the collimator 42 because it reaches the collimator at above the second slot)
• in the example of the figure 3 (c) , almost all of the particles pass through the device (almost all of the particles pass through the first slit, and almost all of the portion of the beam leaving the first collimator passes through the second slit)
• examples of figures 3 (b) and 3 (d) illustrate intermediate situations between situations 3 (a) and 3 (c).

In accordance with the figure 4 , it is possible to obtain at the device output, a variation in the intensity of the beam of charged particles of between 0 and 96% of the beam emitted by the source by varying the intensity U2, with in the example illustrated, the proportion 3U1 = U2.

Voltage change

According to a second possible embodiment, the deflection forces applied by the four successive deflection systems are distinct two by two: 2U1 for the first system, 2U2 for the second system, 2U3 for the third system and 2U4 for the fourth system, with for each system, two lower and upper plates with equal potentials in absolute value and in opposite directions.

$$U2=-U\ast U2a+U2b+B\ast U$$

$$U3=U\ast U3a+U3b+B\ast U$$

$$U4=\frac{-U\ast U4a}{k}+U4b+D\ast U$$

avec :

• U paramètre tension de la chicane en Volt,
• k coefficient sans dimension, qui représente le ratio positif entre la tension appliquée entre les deux plaques extérieures 2₁, 2₄ et celle appliquée entre deux plaques intérieures 2₂, 2₃,
• U1a, U2a, U3a, U4a, U1b, U2b, U3b, U4b, B, D des facteurs de correction en volt.

For example, the voltages U1, U2, U3, U4 can be in the following relationships: $$U1=\frac{U*U1\mathrm{at}}{k}+U1b+D*\mathrm{<figure-callout\; id="2"\; label="U\; U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U\; </figure-callout>}$$

$$U$$$$2=-U*\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}2\mathrm{at}+\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}2b+B*U$$

$$U3=U*U3\mathrm{at}+U3b+B*U$$

$$U4=\frac{-U*U4\mathrm{at}}{k}+U4b+D*U$$

with:

• U baffle voltage parameter in Volt,
• k dimensionless coefficient, which represents the positive ratio between the voltage applied between the two exterior plates 2 ₁ , 2 ₄ and that applied between two interior plates 2 ₂ , 2 ₃ ,
• U1a, U2a, U3a, U4a, U1b, U2b, U3b, U4b, B, D correction factors in volts.

With a coefficient k = 3 the beam must leave the baffle without offset or deviation. To this end, we set U1a, U2a, U2a, U2a each equal to 1 and U1b, U2b, U3b, U4b, B, D set to 0.

The intensity modulation is obtained by partial interception of the beam by the V-slot collimators as described above. The amplitude of the interception depends on the deviation, itself a function of the tension of the chicane 2 _i considered. The correction factors U1a, U2a, U3a, U4a, U1b, U2b, U3b, U4b, B, D are identical for the same voltage parameter U. For example, these correction factors can be set to : k between 2.5 and 3.5; U1a, U2a, U3a and U4a between 0 and 2; U1b, U2b, U3b and U4b between -1000V and + 1000V and B, D between 0 and 2.

Changing the shape of the slots

It is possible to modify the shape of the slots so as to also modify the behavior of the modulation (for example by making the modulation more precise for weak currents). Thus, the opposite sides of the slots could be straight or not, curved curves towards the solid part of the collimator or, on the contrary, curved towards the empty space of the slot. It is expected that the slit of each collimator is offset from the center C to cut the beam at the output when the deflection systems are not supplied.

• ∘ plage de 2µA à 200 µA, avec une précision de 2% :
• ∘ intérêt à avoir une dérivation de la courbe basse pour les faibles intensités d'où profil évasé de la fente, avec pente quasi radiale au centre et ouverture croissante vers la périphérie.
• ∘ Ou fermeture de la fente vers la périphérie pour limiter l'intensité
• ∘ Ou décalage en dessous du centre, pour garantir une intensité minimale même en l'absence de potentiel appliqué aux plaques.

For example, we can provide for the slot:
→ for greater sensitivity for low intensities

• ∘ range from 2µA to 200 µA, with an accuracy of 2%:
• ∘ interest in having a derivation of the low curve for low intensities hence the flared profile of the slit, with almost radial slope in the center and increasing opening towards the periphery.
• ∘ Or closing the slit towards the periphery to limit the intensity
• ∘ Or offset below the center, to guarantee a minimum intensity even in the absence of potential applied to the plates.

The modulation device can be coupled to a current measurement system (of Faraday cage type or non-intersective measurement) positioned downstream of the last deflection system, in order to carry out a precise adjustment of the current by a regulation loop by acting on the deflection force exerted by the deflection systems.

The potentials applied to the deflection plates of the same deflection system can be symmetrical in order to limit the number of power supplies in accordance with the figure 5 (a) (intensity of the collected beam visible on the figure 6a ).

Otherwise, it is possible to use for two plates of the same system, non-symmetrical potentials ( figure 5 (b) : potentials of systems 22 and 23 whose two plates are raised in absolute value to 3500 V and 6500 V respectively), this allowing better beam properties at the output which then fits entirely within a given area ( limitation of emittance and aberrations, see figure 6b ).

Case of a deflection of the incident beam with respect to the axis A0

An alternative embodiment is required if there is an angle of incidence on the beam, a misalignment of the mechanical structure, or an asymmetry of the field, implying that the beam leaves the structure of a baffle with an angle α (U ) with respect to axis A0. The exit angle α (U) of the beam can be a function of the parameter U of the baffle and therefore not constant.

The invention makes it possible to correct this angle of deflection instantly by breaking the symmetry of the voltage applied to the baffle. This is made possible by grounding two or more plates with different voltages U1, U2, U3, or U4 and varying the corresponding correction factor U1b, U2b, U3b, and U4b, respectively.

In the modified configuration of the baffle, each voltage U1, U2, U3, and U4 must remain applied to at least one plate.

The values of the correction factors can be experimentally determined for each defined point of the parameter U of the baffle.

The intensity modulation by the modified baffle is therefore described by I (U, Uib), where Uib are the correction factors with i = 1,2,3,4 of the corresponding voltages Ui for which one of the plates has been set Earth.

Alternatively, it is possible to correct the output angle by applying individual additional adjustable voltages to one or more plates instead of grounding them.

Formulas for this embodiment of the chicane

• U1'=2^∗U1, Si la plaque supérieure 2₄ ou la plaque inférieure 2₁ est mise à la terre.
• U2'=2^∗U2, Si la plaque supérieure 2₃ ou la plaque inférieure 2₂ est mise à la terre.
• U3'=2^∗U3, Si la plaque supérieure 2₂ ou la plaque inférieure 2₃ est mise à la terre.
• U4 '=2^∗U4, Si la plaque supérieure 2₁ ou la plaque inférieure 2₄ est mise à la terre.

Grounding one of the plates requires doubling the tension of the opposite plate to direct the beam through the baffle. The classic chicane formulas can be modified as follows:

• U1 '= 2 ^∗ U1, If the upper plate 2 ₄ or the lower plate 2 ₁ is earthed.
• U2 '= 2 ^∗ U2, If the upper plate 2 ₃ or the lower plate 2 ₂ is earthed.
• U3 '= 2 ^∗ U3, If the upper plate 2 ₂ or the lower plate 2 ₃ is earthed.
• U4 '= 2 ^∗ U4, If the upper plate 2 ₁ or the lower plate 2 ₄ is earthed.

One of the possible practical realizations of the modified baffle would be to ground the upper plates 2 ₁ and 2 ₄ and to double the voltages U1 and U4. The direction introduced by the baffle can be corrected by modifying U1b according to the baffle parameter U: U1b (U). In this case, the intensity modulation by the modified baffle is defined by I (U, U1b (U)).

For example, for this realization and with our specific structure we found the following parameters (U1a = 2, U2a = 1, U3a = 1, U4a = 2, B = D = 0, k = 2.7 are constant) for some measured intensities in the interval between 1 µA and 300 µA: Measured current, I (U, U1b (U)) Baffle tension, U Correction factors, U1b [gA] [V] [V] 296 5000 150 220 4000 30 123 3000 -125 46 2000 -150 23 1500 -170 3 1000 -220

With these values, we found the center of the beam on the beam axis at the position of the measurement plane.

To cover the entire interval without interruption, we must find the relationship Ulb (U) between the correction factor and the tension of the baffle. In the general case it is necessary to find all the relations Uib (U) with i = 1,2,3,4.

Please note that the baffle settings and correction factors are not universally valid and may change for other installations.

Grounding the bottom plates leads to the same result.

It is also possible to apply the voltages in reverse order and to reverse the orientation of the collimators and the sign of the applied voltages. The formulas for the modified chicane remain the same.

Case of eight deflection systems

Furthermore, the device according to the invention may include an additional set of four deflection systems as described above, which will modulate the intensity of the particles in the Y direction shown diagrammatically on the figure 2 . The plates of these deflection systems will then be perpendicular to those of the first set of deflection systems.

Possible dimensions of the device:

80 cm long; 15 cm by 10 cm plate; distance 8 cm between the plates; distance of 3-4 cm between two consecutive plates; side of the slot 4 cm, opening angle 60 °

Possible applications:

Protontherapy, adrontherapy: to irradiate in a controlled manner for each voxel of a tumor for example.

More specifically, the invention finds an application in proton therapy, in particular that using linear accelerators to accelerate proton beams, and in particular using a pulsed proton beam where the invention can be used to modulate or modify the intensity of a proton beam for radiotherapy treatment.

Ion implantation: modulation of the locally implanted dose, depending on the scan
Spectrometry: avoid saturating the detector
Microgravure: modulating the local engraving efficiency during scanning

Claims (13)

1. A device for modulating the intensity of a charged particle beam emitted along an axis (A0), comprising:

   • 4×N consecutive deflection systems (2₁, 2₂, 2₃, 2₄), with N = 1 or 2, with the deflection systems (2₁, 2₂, 2₃, 2₄) being positioned along the axis (A0) of said particle beam, and being capable of deflecting the beam relative to the axis (A0) in the same direction, with alternating directions of deflection, for two consecutive systems (2₁, 2₂, 2₃, 2₄),

   • means for applying a force for deflecting the beam for each deflection system (2₁, 2₂, 2₃, 2₄) and for varying the applied force characterized by

   • two collimators (4₁, 4₂) each having a slot (6₁, 6₂) with an opening that increases in width from the center towards the periphery, located respectively between the first and second deflection systems and between the third and fourth deflection systems, with the opening of the slot (6₁) of the first collimator (4₁) facing towards one side of the emission axis of the beam A0, with the opening of the slot (6₂) of the second collimator (4₁) facing towards the opposite side of the emission axis of the beam (A0).
2. A device according to claim 1 characterized in that each of said deflection systems (2₁, 2₂, 2₃, 2₄) is of the electrical type or of the magnetic type.
3. A device according to claim 2, characterized in that, when the deflection systems (2₁, 2₂, 2₃, 2₄) are of the electrical type, each system (2₁, 2₂, 2₃, 2₄) consists of two parallel plates (7) brought to an electric potential respectively arranged on either side of the emission axis (A0) .
4. A device according to claim 2, characterized in that, when the deflection systems (2₁, 2₂, 2₃, 2₄) are of the magnetic type, each of said deflection systems consists of a magnetic dipole.
5. A device according to one of the preceding claims, characterized in that the slot (6₁, 6₂) of a collimator (4₁, 4₂) has a general V-shape with straight or curved opposite edges domed towards the remaining portion of the collimator (4₁, 4₂) or towards the empty space defined by such edges.
6. A device according to one of the preceding claims, characterized in that each collimator (4₁, 4₂) is placed along the axis so that the slot (6₁, 6₂) thereof is positioned on one side of the emission axis A0 while being offset relative to such axis A0 by a distance d.
7. A device according to one of claims 1 to 5, characterized in that each collimator (4₁, 4₂) is placed along the axis so that the slot (6₁, 6₂) thereof is positioned in line with the emission axis A0.
8. A device according to one of the preceding claims, characterized in that, when it comprises 8 deflection systems (2₁, 2₂, 2₃, 2₄), four of these systems are so arranged relative to the emission axis as to deflect the axis in a first direction, and four of these systems (2₁, 2₂, 2₃, 2₄) are so arranged relative to the emission axis as to deflect the axis in a second direction perpendicular to the first one.
9. A method for deflecting from its emission axis a charged particle beam emitted along an axis A0, with the device according to any one of the preceding claims, characterized in that it comprises, for 4N consecutive deflection systems, a step of application:

   - by the first deflection system (2₁), of a first force for deflecting the beam in a given direction and in a first orientation,

   - - by the second deflection system (2₂), of a second force greater than the first one, for deflecting the beam in the same direction and in an orientation opposite the first one,

   - by the third beam deflection system (2₃), of the second force for deflecting the beam in the same direction and in the first orientation of deflection,

   - by the fourth deflection system (2₄), of the first deflecting force, in the same direction and in an orientation opposite the first one.
10. A method according to claim 9, characterized in that the deflection systems (2₁, 2₂, 2₃, 2₄) are of the electrical type, and each comprise two plates (7) parallel to the axis A0 and arranged on either side of such axis A0, with the potentials applied to the two plates of the same system being symmetrical or asymmetrical.
11. A method according to claim 10, wherein each deflection system is composed of two plates arranged on either side of the axis (A0), with two or more plates of different deflection systems being grounded, with the forces deflecting the beams of the deflection systems of the plates being different, with correction factors (Uib) being applied to each deflecting force imposed on a deflection system, one plate of which is connected to the ground in order to correct the exit angle of the beam.
12. A method according to claim 10, wherein additional adjustable deflection forces are applied to one or more deflection system(s) in order to correct the exit angle of the beam.
13. An assembly for emitting a charged particle beam of adjustable intensity, comprising in succession along an emission axis A0 of the beam:

    - a source of emission of a charged particle beam centered about an emission axis A0, preferably of the ECR type

    - an extraction system

    - a lens of the Einzel type

    - a collimator having a circular central hole

    - the device according to any one of claims 1 to 8,

    - a second collimator having a circular central hole

    - a device speed-filtering the particles at the outlet of the second collimator.

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